Why doesn't the lock screen w/all users showing after booting up?

Just upgraded to Win 10. We have 4 different, non password-protected accounts on our home PC. Before upgrading, the PC used to show a lock-type screen with all 4 accounts straight after booting up. Now, it seems to log on straight away as the person who was last logged on. How can I override this and get Win to show the screen where I can select from all 4 users again?